Heterodyning is a well-established signal processing technique. For example, U.S. Pat. No. 7,860,189 describes hybrid heterodyne transmitters and receivers for use in communications systems, or other systems, and the corresponding methods for hybrid heterodyne transmitting and receiving. A heterodyne receiver for converting a continuous time modulated signal to a discrete time digital baseband signal includes receiving a modulated signal at an RF carrier frequency and provide a quantized output at an intermediate frequency. The digital mixer then provides digital signals representative of a baseband signal suitable for digital signal processing.
As another example, U.S. Pat. No. 6,373,422 describes a radio frequency signal received by an analog-to-digital converter in order to convert the signal from an analog signal into a digital signal. The digital signal is then provided to a decimation filter in order to convert the digital signal into a base band signal. By using a decimation filter the need for a second down conversion mixer is eliminated, thereby eliminating any associated noise, power consumption and distortion associated with using a second mixer.
As yet another example, US Patent Application Publication 2013/0131755 describes a heterodyning architecture applied to convert a selected frequency band of a physiological signal to a baseband for analysis. As an example, the baseband components of the signal may have a frequency in the range of hundreds of Hertz and the carrier frequency is in the range of several kHz. The original baseband components of the signal are chopped to a higher frequency band, e.g., several kHz. Thus, the low-frequency noise signal is segregated from the original baseband components of the signal.